6.s096. Lecture 5. Tuesday, January 22, 13. 1 ... Page 5 ... template
class mypair {. T mypair::getmax(){. T a, b; return a > b ? a : b; public: } mypair(
T ...
6.s096 Lecture 5
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Tuesday, January 22, 13
Today
• C++ (!) • Compiling • Memory management Classes
• • Templates
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Tuesday, January 22, 13
C++
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Tuesday, January 22, 13
C++ • • • • •
Bjarne Stroustrup 1983 Object-oriented (but later than Simula, Smalltalk) Like C, but introduces real objects and classes (plus loads of other features (kitchen sink?))
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Tuesday, January 22, 13
g++ (C++ compiler) •
Very similar to gcc.
#include
g++ -‐o test test.cpp ./test => hi from C++
int main(){
printf("hi from C++\n");
}
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Tuesday, January 22, 13
Wait... was that really C++? • • •
Yes. C++ is pretty close to being a superset of C. We know C, thus we’ll build from that knowledge to learn C++.
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Tuesday, January 22, 13
new memory management syntax
• •
The new operator allocates space on the heap. new and delete take the place of malloc and free. int * numArray = new int[100];
delete numArray;
struct foo * bar = new struct foo; // delete later
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Tuesday, January 22, 13
Classes
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Tuesday, January 22, 13
Why classes? • • •
Modularity Objects (data + behavior) Lets programmers (you) define behavior for your own data
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Tuesday, January 22, 13
Basic Class Example Rectangle::Rectangle(int w, int h){
// constructor definition
width = new int;
height = new int;
*width = w;
*height = h;
}
#include class Rectangle { int * width; int * height;
int main(){
Rectangle box(5, 7);
box.printMe();
}
public: Rectangle(int, int); // constructor ~Rectangle(); // destructor void printMe(){ // 'method' / member function
printf("Dimensions: %d by %d.\n", *width, *height);
}
};
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Tuesday, January 22, 13
Constructors and Destructors •
This destructor should have fit on the last slide...:
•
Since we explicitly allocated something with new, we must also explicitly de-allocate it.
•
Rectangle itself is automatically deallocated when it goes out of scope. 11
Tuesday, January 22, 13
Rectangle::~Rectangle(){ delete width; delete height; }
Default constructors Rectangle::Rectangle(){ width = new int; height = new int; *width = 5; *height = 5; }
// no arguments needed! Rectangle box;
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Tuesday, January 22, 13
Templates • • • • •
Syntax for making code more flexible. Similar in spirit to Java’s generics. Applied at compile-time, like C macros (the preprocessor). Can be applied to classes, functions. Trivia: language of templates is Turing complete.
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Tuesday, January 22, 13
Function Template Example template typeParam max(typeParam a, typeParam b){ return (a > b ? a : b); } int main(){ int a = 3, b = 7; double c = 5.5, d = 1.5; printf("%d\n", max(a, b)); // 7 printf("%f\n", max(c, d)); // 5.5 } 14
Tuesday, January 22, 13
Class Template Example template template
class mypair { T mypair::getmax(){
T a, b; return a > b ? a : b;
public: }
mypair(T first, T second){
a = first; int main(){
b = second; mypair myints(100, 75);
} printf("%d\n",
T getmax(); myints.getmax()); // 100
};
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Tuesday, January 22, 13
MIT OpenCourseWare http://ocw.mit.edu
6.S096 Introduction to C and C++ IAP 2013
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